let arr = [
  {
    age: 10
  },
  {
    age: 20
  }
]
let brr = arr.concat()
console.log(brr);
arr[0].age = 'jfsdjhof'
console.log(brr);


arr.reduce((pre, cur, index, arr) => {
  pre.age = 100
  return pre.age + cur.age
}, {
  age: 99
})
console.log(arr, '====');
